Exercise machines for physical development and rehabilitation uses are well known and take a variety of forms. Typical forms include: user operated free weight machines, such as chest press, shoulder press, etc. on which weights are lifted along a straight line of either standard resistance or variable resistance form; cam operated machines to obtain a desired force curve; machines in which the user exercises against a pneumatic force, etc. Each such machine is designed to exercise one or more groups of muscles of an extremity or part of the body in a certain manner, i.e. to provide resistive force for the user to exercise against in a predetermined and position determined way. The force vs. position relationship is often called the force curve or force profile.
Typically, there are three modes of exercises that a user wishes to perform, these being the isometric, isotonic and isokinetic.
(a) In isometric mode exercises, the rate of angular change or velocity of the part of the body being exercised is zero, while the force can be applied in either of two directions. That is, the exercise is at zero velocity and only heat is developed as the user pushes or pulls against a non-movable object.
(b) In isotonic mode exercises, the load, or resistive force, has a constant value while the velocity varies. Such exercise mode is often performed on a standard resistance weight machine where weight plates are moved up and down a track as the user moves a lifting arm, foot pedal, etc.
(c) In isokinetic mode exercises, the force varies to match t user applied force in such a way that the velocity or force application is kept constant.
Each user desires to perform one or more exercise modes to satisfy different body development or rehabilitation goals. Each exercise would preferably have a force curve individualized for the user to match his goals and his strength capabilities. In the past, where machines using weight plates or friction type devices have been employed, this has required the use of several different types of machines and the mechanical adjustment of the resistive force. Such machines also have restriction in the number of modes and types of exercises that can be performed.
Attempts have also been made to select and control the exercise and its resistive force by the use of computers or microprocessors. See, for example, U.S. Pat. Nos. 4,354,676 to Ariel, 4,063,672 and 3,902,480 to Wilson and 3,869,121 to Flowell; and European Patent Application No. 83301887.2 (Publication 0095832A1). The devices disclosed in these patents and publications have various limitations both in the way in which the resistive force is produced and the variety and types of exercises that can be performed on them.